This invention relates to meters for displaying the operating efficiency of a motor vehicle and in particular to such meters which include a pointer which is movable across an instrument face. A meter of this type is shown in German Utility Model No. 72 42 452 of Nov. 17, 1972.
Engine operating efficiency for an internal combustion engine motor vehicle is generally a function of engine speed. This function includes a region of highest efficiency which occurs at certain engine speeds corresponding to the vehicle cruising speed. The efficiency of the engine becomes lower at both higher and lower engine and vehicle speeds. In the region of highest efficiency, the relationship between the negative pressure in the intake manifold in the engine, commonly used to obtain an engine efficiency reading, and the engine speed is reasonably linear. Disregarding times when the vehicle is stationary, accelerating or decelerating, the operator should, in the interest of minimum fuel consumption and hence also in the view toward environmental conservation, operate the vehicle within the highest efficiency range of the speed curve.
During certain modes of engine operation, efficient operation of the engine is not entirely possible and the engine must operate in other regions of the fuel efficiency curve. Thus, for example, in initial acceleration when the engine is being paced through the various transmission gears, there are rapid changes in engine speed, and hence rapid changes in engine efficiency readings. These transient conditions, which occur during vehicle acceleration, are of only brief duration.
It is also impossible to get a meaningful appraisal of operating efficiency when the engine is idling or when the vehicle is decelerating. In the idling operation, it is particularly inappropriate to display a reading of engine efficiency in terms of consumption per unit distance, since, with the vehicle stationary, any such reading would indicate infinite fuel consumption.
A fuel efficiency instrument which displays operating efficiency of the motor vehicle during all phases of vehicle operation might convey some useful information to the sophisticated vehicle operator, but would only confuse the average motor vehicle operator. Since every instrument reading in a motor vehicle should convey useful information to the vehicle operator, even a layman, without prior study of excess instruction material, such instruments should not display more data than can be used by the average vehicle operator. Such instruments for displaying vehicle operating efficiency should therefore convey enough useful information to the vehicle operator to improve his driving efficiency, but should not display information which would tend to confuse the operator and distract his attention from the road.
It is an object of the present invention to provide an instrument meter for displaying vehicle operating efficiency that is designed in accordance with the psychological and safety considerations such as not to irritate the driver of the vehicle with excess information, and yet provide him with information useful in achieving efficient vehicle operation.